Disc drives are data storage devices that store digital data in magnetic form on a rotating information storage disc. Modern disc drives include one or more rigid discs that are coated with a magnetizable medium and mounted on the hub of a spindle motor for rotation at a constant high speed. For being able to reliably reading and writing information on the disc by means of a read/write head it is critical that the information storage disc is well fixed and centered on the hub of the spindle motor.
Spindle motor assemblies often utilize a rotating spindle hub journaled to a non-rotatable spindle shaft. A disc clamp is typically secured to the rotating spindle hub to exert a downward axial force on the mounted information storage disc in order to securely fasten the disc on the hub. Typically, the disc clamp is basically an annular leaf spring that is sized such that its outer rim exerts the downward force through a series of equally spaced screws positioned around the central portion of the clamp and torqued through holes in a central portion of the clamp into the spindle hub. The spaced radial positioning of the screws is beneficial for exerting a distributed clamping force on the disc on the spindle assembly because the force is exerted at the periphery of the clamp in closer proximity to the mounted information storage disc. However, the screw is a discrete source of the clamping force, thus the distribution of the downward force around the periphery of the clamp, against the adjacent disc is exerted in a non-uniform manner. Non-uniform clamping force can generally cause variations in the load force applied and, as a result, can cause the information storage disc to be physically distorted. Distortion of the disc can lead to generation of unacceptable operational errors during recording and reproduction of data on the information storage disc. Further, the use of screws is relative costly.
In a second type of spindle motor assembly the spindle shaft and spindle hub portion both rotate about a bearing sleeve. Here, a single screw can be used to secure the disc clamp to the rotating spindle shaft because the shaft rotates with the screw, as opposed to the non-rotatable shaft where a plurality of screws must be positioned in the hub about the shaft. However, in order to develop a clamping force with a single screw similar to the force developed by the plurality of screws surrounding the non-rotatable shaft, it is necessary to apply a much higher torque to the single screw. This relatively high torque requirement can lead to a number of problems including over-stressing the spindle shaft bearing, stripping threads, and the generation of particles during the torqueing process. These high-torque related problems can damage the bearing and lead to failure of the spindle motor.
Some screw-less disc clamps have been developed in attempts to overcome these shortcomings, but without completely satisfactory results. Such screw-less disc clamps are disclosed in U.S. Pat. Nos. 6,567,238 B1, 6,417,988 B1, and 6,282,054 B1. Other screw-less solutions are known form U.S. Patent Application Publication Nos. 2001/0036038 A1 or 2002/0071206 A1. Often, such screw-less clamps are complicated, and difficult and expensive to manufacture and to mount on the spindle hub.